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                Expression Serializer Extension
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                Expression Serializer Extension
             

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                Expression Serializer Extension
            
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<div class="section" id="module-sqlalchemy.ext.serializer">
<span id="expression-serializer-extension"></span><h1>Expression Serializer Extension<a class="headerlink" href="#module-sqlalchemy.ext.serializer" title="Permalink to this headline">¶</a></h1>
<p>Serializer/Deserializer objects for usage with SQLAlchemy query structures,
allowing &#8220;contextual&#8221; deserialization.</p>
<p>Any SQLAlchemy query structure, either based on sqlalchemy.sql.*
or sqlalchemy.orm.* can be used.  The mappers, Tables, Columns, Session
etc. which are referenced by the structure are not persisted in serialized
form, but are instead re-associated with the query structure
when it is deserialized.</p>
<p>Usage is nearly the same as that of the standard Python pickle module:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="kn">from</span> <span class="nn">sqlalchemy.ext.serializer</span> <span class="kn">import</span> <span class="n">loads</span><span class="p">,</span> <span class="n">dumps</span>
<span class="n">metadata</span> <span class="o">=</span> <span class="n">MetaData</span><span class="p">(</span><span class="n">bind</span><span class="o">=</span><span class="n">some_engine</span><span class="p">)</span>
<span class="n">Session</span> <span class="o">=</span> <span class="n">scoped_session</span><span class="p">(</span><span class="n">sessionmaker</span><span class="p">())</span>

<span class="c"># ... define mappers</span>

<span class="n">query</span> <span class="o">=</span> <span class="n">Session</span><span class="o">.</span><span class="n">query</span><span class="p">(</span><span class="n">MyClass</span><span class="p">)</span><span class="o">.</span><span class="n">filter</span><span class="p">(</span><span class="n">MyClass</span><span class="o">.</span><span class="n">somedata</span><span class="o">==</span><span class="s">&#39;foo&#39;</span><span class="p">)</span><span class="o">.</span><span class="n">order_by</span><span class="p">(</span><span class="n">MyClass</span><span class="o">.</span><span class="n">sortkey</span><span class="p">)</span>

<span class="c"># pickle the query</span>
<span class="n">serialized</span> <span class="o">=</span> <span class="n">dumps</span><span class="p">(</span><span class="n">query</span><span class="p">)</span>

<span class="c"># unpickle.  Pass in metadata + scoped_session</span>
<span class="n">query2</span> <span class="o">=</span> <span class="n">loads</span><span class="p">(</span><span class="n">serialized</span><span class="p">,</span> <span class="n">metadata</span><span class="p">,</span> <span class="n">Session</span><span class="p">)</span>

<span class="k">print</span> <span class="n">query2</span><span class="o">.</span><span class="n">all</span><span class="p">()</span></pre></div>
</div>
<p>Similar restrictions as when using raw pickle apply; mapped classes must be
themselves be pickleable, meaning they are importable from a module-level
namespace.</p>
<p>The serializer module is only appropriate for query structures.  It is not
needed for:</p>
<ul class="simple">
<li>instances of user-defined classes.   These contain no references to engines,
sessions or expression constructs in the typical case and can be serialized
directly.</li>
<li>Table metadata that is to be loaded entirely from the serialized structure
(i.e. is not already declared in the application).   Regular
pickle.loads()/dumps() can be used to fully dump any <tt class="docutils literal"><span class="pre">MetaData</span></tt> object,
typically one which was reflected from an existing database at some previous
point in time.  The serializer module is specifically for the opposite case,
where the Table metadata is already present in memory.</li>
</ul>
<dl class="function">
<dt id="sqlalchemy.ext.serializer.Serializer">
<tt class="descclassname">sqlalchemy.ext.serializer.</tt><tt class="descname">Serializer</tt><big>(</big><em>*args</em>, <em>**kw</em><big>)</big><a class="headerlink" href="#sqlalchemy.ext.serializer.Serializer" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>

<dl class="function">
<dt id="sqlalchemy.ext.serializer.Deserializer">
<tt class="descclassname">sqlalchemy.ext.serializer.</tt><tt class="descname">Deserializer</tt><big>(</big><em>file</em>, <em>metadata=None</em>, <em>scoped_session=None</em>, <em>engine=None</em><big>)</big><a class="headerlink" href="#sqlalchemy.ext.serializer.Deserializer" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>

<dl class="function">
<dt id="sqlalchemy.ext.serializer.dumps">
<tt class="descclassname">sqlalchemy.ext.serializer.</tt><tt class="descname">dumps</tt><big>(</big><em>obj</em>, <em>protocol=0</em><big>)</big><a class="headerlink" href="#sqlalchemy.ext.serializer.dumps" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>

<dl class="function">
<dt id="sqlalchemy.ext.serializer.loads">
<tt class="descclassname">sqlalchemy.ext.serializer.</tt><tt class="descname">loads</tt><big>(</big><em>data</em>, <em>metadata=None</em>, <em>scoped_session=None</em>, <em>engine=None</em><big>)</big><a class="headerlink" href="#sqlalchemy.ext.serializer.loads" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>

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